The present invention relates generally to ink-jet printers and, more particularly, to a method of detecting poor print quality automatically and taking corrective actions to compensate for such poor print quality. This method is implemented via a print-quality control system which employs optical feedback to read a recently printed image, compares such printed image to a virtual image, and takes corrective action to improve the print quality of subsequently printed images.
Ink-jet printing mechanisms print images on a print medium by firing drops of ink from one or more pens while the pen moves back and forth across the print medium. An ink-jet printer is a device using such ink-jet printing mechanisms. Examples of ink-jet printers include plotters, facsimile machines, and typical computer-attached printers. The print medium on which a printer prints may be any sheet material such as paper, MYLAR(trademark), foils, transparencies, card stock, etc.
Ink-jet printers print dots by ejecting very small drops of ink onto the print medium. The printers typically include a movable carriage that supports one or more pens, each having a printhead with plural ink-ejecting nozzles. The carriage traverses the surface of the print medium, and the nozzles are directed to eject drops of ink at appropriate times pursuant to commands of a microcomputer or other controller. The timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed.
Color ink-jet printers commonly employ a plurality of printheads which may be mounted on the carriage to produce different colors. Each printhead is connected to one or more reservoirs which contain ink for delivery to the printhead""s nozzles. Typically, the reservoirs contain base colors such as cyan, magenta, yellow, and black. Depositing a drop of a base color ink produces a base-colored dot, while depositing multiple drops of different base color inks forms secondary or shaded colors. In other words. the base colors can be combined to form secondary or shaded colors.
Print quality is one of the most important considerations in the use of an ink-jet printer. Although the quality of an image generally is subjective, specific aspects of a printed image can be objectively identified as being indicative of poor print quality. For example, misaligned dots, missing dots, misshapen dots, small dots, large dots, and incorrectly colored dots all are objectively identifiable print errors. Those who are skilled in the art will understand and appreciate that a printed image is of poor print quality if the image exhibits one or more of the above-identified print errors. These errors typically arise from variations or tolerances in the various printing mechanisms or in the printer itself. In addition, various characteristics of the print media may affect print quality. Moreover, environmental conditions, such as temperature and humidity, may affect print quality.
Existing automatic techniques and systems for controlling print quality generally are based upon an estimate of how a specific action may affect print quality. These estimates lack verification of whether corrective action is actually necessary. Also, there is no reliable indication of the extent to which action should be taken to improve print quality. Further, known techniques for controlling print quality do not consider how a printed image actually looks, a factor which should be considered when addressing print quality.
The present invention overcomes the drawbacks and problems of existing print-quality control techniques and systems using an optical system preferably attached to a printhead of an ink-jet printer. The actual printed image thus may be viewed and analyzed and, if it is determined that one or more dots represent poor print quality corrective action may be taken to compensate for the problem so that subsequently-printed dots do not exhibit such poor print quality characteristics.
In one embodiment of the invention, a print-quality control method is employed for use in connection with a printer having a printhead configured to print based on image data. The method includes defining a virtual image derived from the image data, printing an actual image based on the image data, comparing the actual image to the virtual image to identify a printhead error pattern, and modifying subsequent image data to compensate for the identified printhead error pattern.
The invented method may be used in connection with an ink-jet printer which includes a printhead having plural nozzles. The printhead typically receives image signals directing it to print an image, such image being deposited on a print medium by firing the printhead""s nozzles according to the received image signals. The printed image thus will include individual dots printed by the nozzles and may include dots representative of poor print quality due to less-than-optimal operation of the printing mechanisms and/or due to the print medium on which printing occurs.
After printing the image, dots are read by an optical device which preferably is attached to the carriage of the printhead. The optical device produces optical data based on the dots of the printed image and a controller determines whether the printed image includes a poor-print-quality (PPQ) set of dots. If the image does include a PPQ set, then the controller identifies the nozzles which actually printed the PPQ set of dots. Corrective action then may be taken to ameliorate or eliminate the poor-print-quality characteristics of subsequently-printed dots by compensating for the poor print quality of the dots printed by the identified nozzles.
An objective of the present invention is to provide an automatic print-quality control method and system for use in an ink-jet printer where poor print quality will be corrected without the need for user intervention or notification. Another objective is to correct for various types of poor print quality by viewing actually printed dots with an optical device and correcting for observable objective print quality problems.
These and other objects and advantages of the present invention will be more readily understood after a consideration of the drawings and the detailed description of the preferred embodiment which follows.